Remove .values in _slice_from_grid (#890)

Collecting values after isel in _slice_from_grid needs to be avoided to
keep the data in xarray/dask.

Fix #889

Co-authored-by: Philip Chmielowiec <67855069+philipc2@users.noreply.github.com>

uxarray/core/dataarray.py

@@ -1077,17 +1077,17 @@ def _slice_from_grid(self, sliced_grid):
         if self._face_centered():
             d_var = self.isel(
                 n_face=sliced_grid._ds["subgrid_face_indices"], ignore_grid=True
-            ).values
+            )
 
         elif self._edge_centered():
             d_var = self.isel(
                 n_edge=sliced_grid._ds["subgrid_edge_indices"], ignore_grid=True
-            ).values
+            )
 
         elif self._node_centered():
             d_var = self.isel(
                 n_node=sliced_grid._ds["subgrid_node_indices"], ignore_grid=True
-            ).values
+            )
 
         else:
             raise ValueError(